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What is the VFD RS485 Communication Error on my NetworkAIR FM/IR40?

"In controller firmware v6.11.0 a new feature was added to generate alarms on loss of communications with the VFDs. The FM controller continuously polls data from the VFDs, one data point at a time. There is an error counter for each piece of data. The error counter is incremented if the FM controller receives either an incorrect response or no response to a query; else the error counter is decremented. When the error on any one piece of data reaches the value of three, then the alarm is generated. The alarm is cleared when the error counts of all data items have a value of zero. The error count is never allowed to go below zero or above three.

One possibility is that SW2, located under the RJ45 connector on the VFD, needs to be in the ON position. It is also possible that one or both VFDs have the wrong address programmed into them. To check this you'll need to connect the VFD keypad to each VFD and check the value of parameter H31. The leftmost VFD should have a value of 1 and the other should have a value of 2.